1. Field Of The Invention
The present invention generally relates to headboxes for fourdrinier papermachines. More particularly, the invention is directed to a method and apparatus for generating a positively controlled degree of micro-scale turbulence in the headbox slice discharge jet.
2. Description Of The Prior Art
Paper and other non-woven webs of fibrous material are traditionally made by depositing a fluidized suspension of fiber such as cellulose pulp, called stock, onto a traveling forming screen characterized as a fourdrinier wire. The rate and distribution of stock deposition upon such a fourdrinier wire is controlled by a headbox assembly which comprises a slice channel opening for discharging an elongated jet of stock onto the moving screen. Liquid vehicle of the suspension, usually water, drains through the screen openings leaving the fiber constituent of the suspension on the screen surface as an accumulated mat.
In an aqueous suspension, cellulose fibers have a considerable affinity to agglomerate into clusters called flocs. This occurs in the system piping and flow channels prior to the headbox. Notwithstanding repeated agitation and mixing to disperse flocs prior to deposit on the screen, many remain to be set into the web formation. These are seen in the finished paper product as a mottled pattern of birdseyes and dark or dense spots or areas. Such non-uniformity of fiber distribution is the source of numerous paper converting and printing difficulties.
Several devices and techniques are used, have been used or proposed to disperse flocs prior to setting on the screen. The commonly used headbox holey-roll is representative. The objective in all such proposals is to induce a high degree of micro-scale turbulence across the span of the discharge jet for floc dispersion. Fluid and boundary layer shear are the usual energy source of such turbulence. For example, white water or low consistency stock may be discharged from numerous sources around the slice nozzle at high velocity into the headbox final flow channel prior to the slice.
Efficient generation of micro-scale turbulence in a headbox slice flow stream is therefore one objective of the present invention. This is accomplished in a manner similar to that disclosed by U. S. Pat. No. 2,904,461 wherein numerous jet sources of white water or thin stock are discharged into the headbox from the front wall thereof and in a counter flow direction to the stock within the headbox.
An additional objective of the present invention is to teach a convenient structure by which such fresh or white water jets are integrated into the headbox assembly.
Another objective of the present invention is to teach the construction of a malleable slice profile bar having integral discharge jets for turbulence generation and floc dispersion.
Another objective of the present invention is to teach a fluid distribution system for headbox turbulence generation that may be added as a post-construction accessory to most existing headboxes of prior art construction.